1. Field of the Invention
This invention pertains to normalizing and more particularly to automatically normalizing to a master channel of a multi-channel sorting apparatus for processing relatively large quantities of fungible products and rejecting non-standard products.
2. Description of the Prior Art
A typical color food sorting machine consists of many different components in order to electronically discriminate unacceptable from acceptable food products and mechanically separate (i.e. sort) the bad from the good. These components are generally comprised of one or more lighting illumination sources; optical assemblies for viewing, focusing, and light wavelength filtering; photocell detectors for converting light energy into electricity; and various electronic circuits for amplifying, conditioning and classifying resultant signals into acceptable and unacceptable occurrences. For multiple channel sorting machines, multiple sets of these various components are packaged into one machine.
A description of one type of normalizing for such a machine is described in commonly assigned U.S. Pat. No. 4,626,677, "Continuous Normalizer for an Electronic Circuit that Compensates for External and Internal Drift Factors", Edward M. Browne, issued Dec. 2, 1986, which patent is incorporated herein by reference for all purposes. Although the circuit operation therein described is suitable for continuously normalizing and thereby stabilizing the operation of a single channel, it is very common to have multiple channels in a single machine that are each independently operating and normalizing only to what occurs in their respective channels.
In the ideal sorting machine, each of the various components are identically matched to each other and packaged with absolute precision that result in each channel's classification discrimination capability of identical good and bad products being exactly the same. Great effort and expense is devoted in the design, testing qualification, and manufacture of sorting machines to achieve this perfect assembly of matched components. However, practical machines are never made with perfect components. Each of the various machine components have inherent subtle variations in their performance parameters that result in each channel having similar, but never identical, classification discrimination capability.
Typical corrective techniques that have historically been used include potentiometer adjustment of signal gains and nulls, and electronic storage and comparison of signal characteristics to a set of known good signals. Although these techniques have greatly improved overall machine performance on initial adjustment, nothing stays the same for long.
Over a period of time, machine performance degrades due to aging of the lamps and electronic components, subtle shifts of product color and hue, differences in product batches and differences in product conveyance characteristics. To correct this degradation, the user must shut the machine down and have a human operator and/or technician readjust and/or calibrate the machine for desired performance. To prolong the period between readjustment and/or calibration, the continuous normalizer described in U.S. Pat. No. 4,626,677 was developed. However, the normalizer operation described in the '677 patent does not normalize to a single channel. Therefore, in a multi-channel machine, the readjustment and/or calibration requirements to prevent a wide disparity in rejection rate from developing from channel to channel still leads to costly downtime, lost production capacity, and high maintenance expense.
In the multi-channel machines currently in use, there is an adjustable potentiometer or the like for each channel that is included in the discrimination circuit. A human operator or technician observes the operation and if it appears to him that a particular channel is rejecting more or less of the products than the other channels, he trims or "tweeks" the adjustment on that channel to bring it back in line. To periodically make such fine tune adjustments in response to visually determining if the ejectors are firing at similar rates is extremely tedious and uncertain in result when there are a large number of channels. There are machines with up to 128 channels in use today.
A technique has recently been conceived to help achieve uniformity of detection among multiple channels. A single channel out of a group of similar channels is designated as the "master" or calibration channel. A single analog reference generates the discrimination or "trip level" reference signal, which is routed to all channels. However, because of the limitations of a number of factors such as light intensity or amplifier gain, the trip level for the non-master or "slave" channels is likely to be somewhat in error. That is, even though the trip level for a slave channel is exactly the same as for its master channel, the discrimination characteristics will likely be different.
Therefore, it is a feature of the present invention to provide an automatic ejector rate normalizer that assures that the ejector rate for each of the slave channels tracks the ejector rate for the master channel.
It is another feature of the present invention to provide an automatic ejector rate normalizer that includes a counter for the master channel ejector portion and assures that each of the slave channels is automatically adjusted to continuously eject "bad" products at the same rate by count as the master channel ejector.
It is still another feature of the present invention to provide automatic detection sensitivity correction to channel ejection circuitry as determined by digital correction from the master channel of the analog trip level signal respectively supplied to each slave channel.